The new Spiraea cultivar is the product of a planned breeding program conducted by the inventor, Timothy D. Wood, in Grand Haven, Mich. The objective of the breeding program was to produce new Spiraea varieties of compact and full habit with novel and improved flower and leaf colors. The open pollination resulting in this new variety was made during June of 2004.
The seed parent is the commercial variety, Spiraea japonica ‘Walbama’ U.S. Plant Pat. No. 9,363. The pollen parent is unknown as it was an open pollination breeding program. The new variety was identified as a potentially interesting selection in June of 2006, at a nursery in Grand Haven, Mich.
Asexual reproduction of the new cultivar ‘SMSJDG603’ by softwood cuttings was first performed during June of 2006, at commercial greenhouse in Grand Haven, Mich. Subsequent propagation has shown that the unique features of this cultivar are stable and reproduced true to type in 6 successive generations.